1. Field of the Invention
This invention relates to a granulating and coating machine, more particularly to a granulating and coating machine which is capable of granulating, coating, mixing, and drying granular and powdery raw materials with high productivity.
2. Prior Art
Granulation is one of the most useful way of processing products from the pharmaceutical industry and some others, too. But it has long been the most difficult process. In order to perform granulation, many trials were made and traditional methods were developed. However, each unit process requires different unit equipment. Of course, skilled workers were also required in each unit process. Thus, the traditional granulation is very low in productivity, very difficult in technology and not suitable for GMP (Good Manufacturing Practice).
Some decade ago, the fluidized bed granulation method was developed as a quite new process. This method excludes wetting/kneading, cutting and tumbling, though it includes mixing and drying. A single piece of equipment, the fluidized bed granulator, is required, but nothing more. It is suitable for GMP.
While raw material powders are fluidized by an air stream in this equipment, they are sprayed by a binder solution. The particles receiving droplets of the solution agglomerate with others and enlarge their size. At the same time, the agglomerated particles are dried by the air stream for fluidization. Since the air required for fluidization is far more than the air for drying, the enlarged particles are dried almost instantaneously.
Fluidized bed granulation seemed to be a perfect method. However, it has big disadvantages in technique and in quality of the product. Fluidization is performed by virtue of the balance of lifting force of air and gravity on the particles. The balance easily tends to be loosen especially the particles' size, shape and weight are changed during fluidization. This is the basic difficulty of fluidized bed granulation. Furthermore, the concentration of particles should be lowered to avoid any interaction between them and keep a good fluidizing state. But it makes the space yield of fluidization granulation very low. Qualitywise, enlarged particles obtained by this method are generally very bulky, coarse and brittle, due to the lack of kneading and tumbling.
In the prior art, there were provided many types of machines for granulating, coating, mixing, and drying granular and powdery materials for use in the fields of medicine, foods, powdered metals, catalyst, ferrite, ceramics, detergent, cosmetics, dyestuff, pigment, toner, etc.
As one example of such prior machines, there was provided a machine which had a mesh at the bottom of a granulating casing and rotary blades mounted over the mesh. This prior machine, however, was not suitable for granulation and coating, because the granulated materials were disintegrated by the rotary blades and the mesh to make it impossible to obtain spherical products. In addition, the coated film was flawed.
There is disclosed another prior machine having a rotary plate or disk over a mesh provided at the bottom of a granulating casing, this is shown in the Japanese Patent Laid-open Publications Nos. 54-62978 nd 56-133024. This prior art device can be used for granulation and coating, but it has a drawback in that the granulated materials are caught between the rotary disk and the mesh so as to be disintegrated by being rubbed against the mesh when the rotary disk is rotated. In this prior art, another drawback that should be mentioned is that the powdery materials are leaked through the mesh. In addition to these drawbacks, this prior art can not control the bulk density of the granulated materials, as the result of this, it is able to granulate only heavy products with irregular particle size. Further, the prior art machine has another defect in that the productivity of the prior machine is low.
In the Japanese Patent Publications Nos. 46-22544 and 47-47794, there is disclosed a coating machine wherein the bottom wall of the casing is formed by a rotary disk, and coating is performed by the centrifugal tumbling obtained by the rotation of the rotary disk and the air introduced through the slit formed between the outer periphery of the rotary disk and the inner wall of the casing. This prior machine is, however, constructed mainly for coating, and when it is used for granulation, the productivity is low because of less drying capacity and blocking of granules. Therefore, this prior art is unsuitable for mass granulation. Further, this prior art produces only heavy spherical products, but does not produce light products.